As disclosed by Ball et al. in U.S. Patent Publication No. U.S. 2008/0188936A1 and illustrated in FIG. 1, the rotator cuff 10 is the complex of four muscles that arise from the scapula 12 and whose tendons blend in with the subjacent capsule as they attach to the tuberosities of the humerus 14. The subscapularis 16 arises from the anterior aspect of the scapula 12 and attaches over much of the lesser tuberosity. The supraspinatus muscle 18 arises from the supraspinatus fossa of the posterior scapula, passes beneath the acromion and the acromioclavicular joint, and attaches to the superior aspect of the greater tuberosity 11. The infraspinatus muscle 13 arises from the infraspinous fossa of the posterior scapula and attaches to the posterolateral aspect of the greater tuberosity 11. The teres minor 15 arises from the lower lateral aspect of the scapula 12 and attaches to the lower aspect of the greater tuberosity 11. Proper functioning of the rotator depends on the fundamental centering and stabilizing role of the humeral head 15 with respect to sliding action during anterior and lateral lifting and rotation movements of the arm.
The insertion of these tendons as a continuous cuff 10 around the humeral head 17 permits the cuff muscles to provide an infinite variety of moments to rotate the humerus 14 and to oppose unwanted components of the deltoid and pectoralis muscle forces. The insertion of the infraspinatus 13 overlaps that of the supraspinatus 18 to some extent. Each of the other tendons 16, 15 also interlaces its fibers to some extent with its neighbor's tendons. The tendons splay out and interdigitate to form a common continuous insertion on the humerus 14.
The rotator cuff muscles 10 are critical elements of this shoulder muscle balance equation. The human shoulder has no fixed axis. In a specified position, activation of a muscle creates a unique set of rotational moments. For example, the anterior deltoid can exert moments in forward elevation, internal rotation, and cross-body movement. If forward elevation is to occur without rotation, the cross-body and internal rotation moments of this muscle must be neutralized by other muscles, such as the posterior deltoid and infraspinatus. The timing and magnitude of these balancing muscle effects must be precisely coordinated to avoid unwanted directions of humeral motion. Thus the simplified view of muscles as isolated motors, or as members of force couples must give way to an understanding that all shoulder muscles function together in a precisely coordinated way—opposing muscles canceling out undesired elements leaving only the net torque necessary to produce the desired action. Injury to any of these soft tissues can greatly inhibit ranges and types of motion of the arm.
The mechanics of the rotator cuff 10 are complex. The cuff muscles 10 rotate the humerus 14 with respect to the scapula 12, compress the humeral head 17 into the glenoid fossa providing a critical stabilizing mechanism to the shoulder (known as concavity compression), and provide muscular balance. The supraspinatus and infraspinatus provide 45 percent of abduction and 90 percent of external rotation strength. The supraspinatus and deltoid muscles are equally responsible for producing torque about the shoulder joint in the functional planes of motion.
With its complexity, range of motion and extensive use, a fairly common soft tissue injury is damage to the rotator cuff or rotator cuff tendons. Damage to the rotator cuff is a potentially serious medical condition that may occur during hyperextension, from an acute traumatic tear or from overuse of the joint. With its critical role in abduction, rotational strength and torque production, the most common injury associated with the rotator cuff region is a strain or tear involving the supraspinatus tendon. A tear in the supraspinatus tendon 19 is schematically depicted in FIG. 2. A tear at the insertion site of the tendon with the humerus, may result in the detachment of the tendon from the bone. This detachment may be partial or full, depending upon the severity of the injury. Additionally, the strain or tear can occur within the tendon itself. Injuries to the supraspinatus tendon 19 and recognized modalities for treatment are defined by the type and degree of tear. The first type of tear is a full thickness tear as also depicted in FIG. 2, which as the term indicates is a tear that extends through the thickness of the supraspinatus tendon regardless of whether it is completely torn laterally. The second type of tear is a partial thickness tear which is further classified based on how much of the thickness is torn, whether it is greater or less than 50% of the thickness.
The accepted treatment for a full thickness tear or a partial thickness tear greater than 50% includes reconnecting the torn tendon via sutures. For the partial thickness tears greater than 50%, the tear is completed to a full thickness tear by cutting the tendon prior to reconnection. In treating a full thickness tear or partial thickness tear of greater than 50% after completing the tear by cutting the tendon, accepted practice also can include the placement of scaffolds and patches over the repaired tendon to shield the sutured or repaired tendon area from anatomical load during rehabilitation. For example, Wright Medical disclose that the GraftJacket® can be used to augment a suture repaired tendon in large and massive full-thickness tears or smaller full-thickness tears in a shoulder having severely degenerated tissue. However, it is recognized that significant shielding of the tendon from load can lead to atrophy and degeneration of the native tendon and muscle.
It is known that, for the rotator cuff, allowing the tendon to experience full anatomical load during recovery after repairing the tendon tear with sutures will result in a 20-60% failure rate. Ball et al. (U.S. Patent Appl. No. 2008/0188936 A1) disclose an implant that provides a healing modality that shields the tendon from most of the anatomical loads in the early part of the recovery period, and gradually experience increasing loads as the repair heals to full strength. Ball et al. discloses the strength of the surgical repair, expressed as percent strength of the final healed repair, begins post-surgically at the strength of the suture-to-tissue connection alone. In their illustrated example, the suture-to-tissue connection represents about 25% of the strength. The augmentation implant initially receives the 75% of the loads experienced during recovery through high initial strength. Gradually, the ratio of load sharing shifts to the suture-to-tissue connection as the repair heals and gains strength, while the implant is simultaneously absorbed by the body. Strength retention is defined to refer to the amount of strength that a material maintains over a period of time following implantation into a human or animal. For example, if the tensile strength of an absorbable mesh or fiber decreases by half over three months when implanted into an animal or human, the mesh or fiber's strength retention at 3 months would be 50%.
In contrast to the treatment of a full thickness tear or a partial thickness tear of greater than 50%, the treatment for a partial thickness tear less than 50% usually involves physical cessation from use of the tendon, i.e., rest. Specific exercises can also be prescribed to strengthen and loosen the shoulder area. In many instances, the shoulder does not heal and the partial thickness tear can be the source of chronic pain and stiffness. Further, the pain and stiffness may cause restricted use of the limb which tends to result in further degeneration or atrophy in the shoulder. Surgical intervention may be required for a partial thickness tear of less than 50%. However, current treatment interventions do not include repair of the tendon. Rather, the surgical procedure is directed to arthroscopic removal of bone to relieve points of impingement or create a larger tunnel between the tendon and bone that is believed to be causing tendon damage. As part of the treatment, degenerated tendon may also be removed using a debridement procedure. Again, the tendon partial tear is not repaired. Several authors have reported satisfactory early post-operative results from these procedures, but over time recurrent symptoms have been noted. In the event of recurrent symptoms, many times a patient will “live with the pain”. This may result in less use of the arm and shoulder which further causes degeneration of the tendon and may lead to more extensive damage. A tendon repair would then need to be done in a later procedure if the prescribed treatment for partial tear was unsuccessful in relieving pain and stiffness or over time the tear propagated through injury or degeneration to a full thickness tear or a partial thickness tear greater than 50% with attendant pain and debilitation. A subsequent later procedure would include the more drastic procedure of completing the tear to full thickness and suturing the ends of the tendon back together. This procedure requires extensive rehabilitation, has relatively high failure rates and subjects the patient who first presented and was treated with a partial thickness tear less than 50% to a second surgical procedure.
As described above, adequate treatments do not currently exist for repairing a partial thickness tear of less than 50% in the supraspinatus tendon. Current procedures attempt to alleviate impingement or make room for movement of the tendon to prevent further damage and relieve discomfort but do not repair or strengthen the tendon. Use of the still damaged tendon can lead to further damage or injury. Prior damage may result in degeneration that requires a second more drastic procedure to repair the tendon. Further, if the prior procedure was only partially successful in relieving pain and discomfort, a response may be to use the shoulder less which leads to degeneration and increased likelihood of further injury along with the need for more drastic surgery. There is a large need for surgical techniques and systems to treat partial thickness tears of less than 50% and prevent future tendon damage by strengthening or repairing the native tendon having the partial thickness tear.